1. Field of the Invention
The present invention pertains to a tracheotomy valve and, in particular, to an improved unidirectional tracheotomy valve that is easily actuated to close even by patients having relatively low tidal volumes and that operates reliably even if the patient is inclined from vertical over a range of angles.
2. Description of the Related Art
Unidirectional tracheotomy valves that are adapted to be mounted on the end of a cannula, which is inserted into the patient's trachea, are known, in general. Such valves allow air to flow through the cannula and into the lungs during inspiration and prevent air from flowing through the cannula during expiration. Thus, during expiration, air flows through the patient's upper airways, such as the subglottic trachea, larynx, pharynx, mouth, and nasal passages. As a result, tracheotomized individuals using a unidirectional tracheotomy valve are able to communicate orally and maintain clear upper airway passages by coughing or expelling air through the upper airway passages. Maintaining clear upper airway passages is important for safe oral alimentation as well as to prevent dystrophy of the muscles in the upper airways, for example.
FIGS. 1a-1c illustrate an original model of a unidirectional ball-valve assembly developed by the present inventors. In this device, a ball 20 is provided within a chamber 22 of housing 24, which includes a first opening 26 and a second opening 28 at either end of chamber 22. Housing 24 is attached to a cannula 30, which is inserted into the patient's trachea 32. During inspiration, as illustrated in FIG. 1b, air is drawn into chamber 22 through first opening 26, causing ball 20 to move to a second position proximate to second opening 28, being kept from occluding opening 28 by a thin wire stop (identified by numeral 27 in FIGS. 1a-1c). Thereafter, air flows through chamber 22 to the patient's lungs via cannula 30, as indicated by arrows 34. During expiration, as illustrated in FIG. 1c, air is forced into chamber 22 through second opening 28 causing ball 20 to move to a first position blocking first opening 26. As a result, air expelled from the patient's lungs does not pass through cannula 30, but instead is provided to the patient's upper airways as indicated by arrows 36. See FIG. 1c.
In order to block first opening 26 during expiration, ball 20 must traverse a distance d as illustrated in FIG. 1c. However, moving ball 20 distance d requires a relatively large expiration force. Consequently, some patients, especially those patients having relatively small tidal volumes, may not have a tidal volume and expiration force sufficient to block the first opening as air is expelled from the lungs. Furthermore, even in patients having larger tidal volumes, there is a fraction of a second delay after expiration is initiated before a sufficient expiration force is built up to move ball 20 into first opening 26 thereby enable phonation. This delay is sufficient to cause the leading syllable of a patient's utterance to be truncated or suppressed.
An improved unidirectional tracheotomy valve also developed by the present inventors is illustrated in FIGS. 2a-2c. This tracheotomy valve improves upon the conventional tracheotomy valve illustrated in FIGS. 1a-1c because less expiration force is required to close the valve and the delay before phonation commences is reduced to virtually zero, allowing speech to sound more natural. These improvements are achieved by eccentrically locating first opening 26a at the end of housing 24 such that a central axis 38 of first opening 26a is aligned with the center of ball 20. Because first opening 26a is eccentrically located on the end of housing 24, ball 20 does not need to be raised a distance d in order to block first opening 26a.
During inspiration, as illustrated in FIG. 2b, this tracheotomy valve functions in the same manner as the tracheotomy valve discussed above with respect to FIGS. 1a-1c. That is, air is drawn into chamber 22 causing ball 20 to move to a second position so that air flows through housing 24, cannula 30 and into the patient's lungs, as indicated by arrows 34. However, during expiration, which is illustrated in FIG. 2c, air is expelled from the lungs and enters chamber 22 causing ball 20 to roll directly into first opening 26a thereby blocking first opening 26a. When first opening 26a is blocked, air does not flow through housing 24 and cannula 30, but, instead, is provided to the patient's upper airways.
It has been found that the device illustrated in FIGS. 2a-2c functions adequately when the patient is in a vertical position. However, this device does not function reliably if the patient is reclined more than 20 degrees from vertical because the ball must move uphill against gravity. In addition, to function properly, housing 24 must be carefully positioned such that first opening 26a is located in the lower central portion of the end of the housing so that ball 20 rolls directly into the second opening.